Environmentally persistent free radicals (EPFRs) are produced during biochar pyrolysis and, depending on biochar application, can be either detrimental or beneficial. High levels of EPFRs may interfere with cellular metabolism and be toxic, because EPFR-generated reactive oxygen species (e.g., hydroxyl radicals (•OH)) attack organic molecules. However, •OH can be useful in remediating recalcitrant organic contaminants in soils. Understanding the (system-specific) safe range of EPFRs produced by biochars requires knowing both the context of their use and their overall significance in the existing suite of environmental radicals, which has rarely been addressed. Here we place EPFRs in a broader environmental context, showing that biochar can have EPFR concentrations from 10⁸-fold lower to 10⁹-fold higher than EPFRs from other environmental sources, depending on feedstock, production conditions, and degree of environmental aging. We also demonstrate that •OH radical concentrations from biochar EPFRs can be from 10⁴-fold lower to 10¹⁷-fold higher than other environmental sources, depending on EPFR type and concentration, reaction time, oxidant concentration, and extent of environmental EPFR persistence. For both EPFR and •OH concentrations, major uncertainties derive from the range of biochar properties and the range of data reporting practices. Controlling feedstock lignin content and pyrolysis conditions are the most immediate options for managing EPFRs. Co-application of compost to provide organics may serve as a postpyrolysis method to quench and reduce biochar EPFRs.

中文翻译：

---

生物炭中的环境持久性自由基：环境背景和未来研究需求

环境持久性自由基 （EPFR） 是在生物炭热解过程中产生的，根据生物炭的应用，可能是有害的，也可能是有益的。高水平的 EPFR 可能会干扰细胞代谢并具有毒性，因为 EPFR 产生的活性氧（例如羟基自由基 （•OH））会攻击有机分子。然而，•OH 可用于修复土壤中的顽固有机污染物。了解生物炭产生的 EPFR 的（系统特定的）安全范围需要了解它们的使用背景以及它们在现有环境自由基套件中的整体意义，而这很少得到解决。在这里，我们将 EPFR 置于更广泛的环境背景下，表明生物炭的 EPFR 浓度可以比其他环境来源的 EPFR 低 10⁸ 倍到 10⁹ 倍，具体取决于原料、生产条件和环境老化程度。我们还证明•生物炭 EPFR 的 OH 自由基浓度可以比其他环境来源低 10⁴ 倍到 ^{10 17} 倍，具体取决于 EPFR 类型和浓度、反应时间、氧化剂浓度和环境 EPFR 持久性的程度。对于 EPFR 和 •OH 浓度，主要不确定性来自生物炭特性的范围和数据报告实践的范围。控制原料木质素含量和热解条件是管理 EPFR 的最直接选择。堆肥的共同应用以提供有机物可以作为淬火和减少生物炭 EPFR 的后热解方法。